I think the whole benefit of a fast is autophagy. You put your body in a position where it has no choice but to scavenge its cells for basic resources. the bad and weak cells go first, as well as the fat cells. This is especially true with dry fasting, where you now add water to the main reasons to go after bad/weak/fat cells. I would imagine that anything you take to slow this down, be it a multi-vitamin or ACV, gets in the way of this process. Maybe you save the ACV/Lemon/Vitamins/whatever until you break the fast.